1. Field of the Invention
The present invention relates to the structure of a light source unit which is employed in a multiple beam scanning recorder.
2. Description of the Background Art
In an image scanning recorder such as a color scanner, multiple beams which are modulated by recording signals are scanned simultaneously on a recording medium in order to improve a recording speed. At this time, the multiple beams are implemented by arranging a plurality of light emitting devices such as laser diodes or light emitting diodes along a constant direction.
FIGS. 12(a) and 12(b) illustrate arrangements of such light emitting devices. Referring to FIG. 12, an arrangement of beams b.sub.1 to b.sub.5 shown at (a) is attained when five light emitting devices are arranged in a subscanning direction Y at regular intervals A. This arrangement is simple and widely applied in the art.
On the other hand, an arrangement shown at (b) in FIG. 12 is attained by improving the arrangement (a), in order to further reduce the beam-to-beam intervals. Namely, five light emitting devices (five beams b.sub.1 to b.sub.5) are arranged at regular intervals A' (&lt;A) in a direction inclined by an angle .theta. with respect to a main scanning direction X.
U.S. Pat. No. 4,253,102 discloses a beam arrangement which is similar to the arrangement (b). According to this technique, respective light emitting devices are arranged on a straight line, which is inclined by an angle .theta. with respect to a subscanning direction, at regular intervals. This technique is aimed at arranging beams so that no clearances are defined between the respective beam spots .when the beams are scanned in the main scanning direction. In this technique, therefore, it is necessary to arrange the light emitting devices so that adjacent ones of the light emitting devices or the beams are necessarily in contact with each other, as well as to expose a photosensitive film while finally maintaining the state of the beam arrangement which is inclined by the angle 0 with respect to the subscanning direction. Due to such characteristics, this technique attains its specific object.
The aforementioned technique can be regarded as useful when the number of the beams is relatively small. When the number of the beams is increased to more than ten due to requirement for further improvement of the recording speed, however, a light source part is increased in dimension in proportion to the number of beams in the beam arrangement according to this technique, leading to such a problem that this part cannot practically serve as a light source for a scanning recorder. In a general scanning recorder, beam-to-beam intervals between multiple beams which are emitted from a light source part are reduced to prescribed values through a reduction optical system so that the reduced beams are scanned on an exposed film. Therefore, the light source part is naturally limited in size in response to the size of an employable reduction optical system (lenses).
Thus, awaited is implementation of a light source part (or a light source unit) which is also applicable to a multi-channel type scanning recorder employing 80 beams, for example.